| Cover | Sep. 15, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Sep. 15, 2023 |
| Entity Registrant Name | XENCOR, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36182 |
| Entity Tax Identification Number | 20-1622502 |
| Entity Address, Address Line One | 465 North Halstead Street |
| Entity Address, Address Line Two | Suite 200 |
| Entity Address, City or Town | Pasadena |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 91107 |
| City Area Code | (626) |
| Local Phone Number | 305-5900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | XNCR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001326732 |
